Disturbance off Florida coast has high chance of development, NHC says

PM UPDATE: The National Hurricane Center increased the chances of development of the system off Florida’s coast to 60 percent over the next two days and 80 percent over the next five days. Satellite imagery shows the first rains association with 91L moving into the northern Bahamas as it moves south-southwest. Forecasters said that the circulation was “gradually becoming better defined.”

Palm Beach International Airport had 0.61 of an inch of rain from storms that set up along the coast from 2-3 p.m. A weather station in Palm Beach recorded 0.48 of an inch through 3 p.m.

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ORIGINAL POST: July is usually a drier month in South Florida as the unsettled weather of June fades and a more typical summer weather pattern takes hold. But this year the new month could start out with a bang — if the area of low pressure off Florida’s East Coast revs up enough to deliver a multi-day soaking to the peninsula.

Meteorologists at the National Weather Service in Miami and at the National Hurricane Center were busy slicing and dicing data from disturbance 91L today, looking for clues on how strong the low may get and where it might go. Uncertainty, NWS forecasters said in their morning analysis, “is high. The strength and location of the area of low pressure will determine overall rainfall chances and amounts.”

In addition to rainfall amounts across Central and South Florida, the big question is whether the disturbance will become the Atlantic season’s first tropical depression, or Tropical Storm Arthur, sometime this week. NHC forecasters say those chances are high — 70 percent — over the next five days. And there’s a 40 percent chance of development over the next two days.

At 5 a.m., 91L was 269 miles north-northeast of Palm Beach with top winds of 23 mph. It was moving to the south, and pressure remained high at 1016 mb.

Development was being inhibited by dry air to the north, and upper level winds were only marginally favorable for development, according to NHC Senior Hurricane Specialist Stacy Stewart.

“By Wednesday, however, environmental conditions are expected to become more conducive for development of this system while it drifts southward and meanders offshore of the Florida east coast,” Stewart wrote in his tropical weather outlook today. By that time, according to the European forecast model, 91L may be on its way north again, strengthening as it moves up the coast toward the Carolinas.

Rainfall totals are notoriously difficult to predict, especially when a potential tropical system lurks in the vicinity. The NWS’ Weather Prediction Center, which has the difficult task of projecting rainfall amounts, shows 3.74 inches falling through Wednesday just north of Grand Bahama Island, with perhaps up to 2 inches in Palm Beach and areas east and north of Lake Okeechobee.

AccuWeather’s forecast calls for 1.29 inches in and around Palm Beach through Wednesday.

Forecasters at Weather.com (The Weather Channel) warn that Florida’s southeast coast could get slammed with strong rip currents and high surf, in addition to the potential for heavy rain.

The NWS forecast is for a 40 percent chance of rain today, 50 percent on Monday, 60 percent on Tuesday and 50 percent on Wednesday. The reasoning is that storms that form over the peninsula will be pushed south and east as the area begins to fall under the influence of the counter-clockwise circulation of 91L.

By Wednesday or Thursday, the system may leave drier weather in its wake if it does in fact head back to the north. The July 4 forecast is for partly sunny skies in Palm Beach with a 30 percent chance of rain.

About the Author

John Nelander is a freelance writer, book editor and publisher in West Palm Beach. Weather Matters features news and observations about the weather with a focus on what's happening in South Florida. The blog also looks at the latest studies on climate change as well as what's happening in the weather forecasting biz. His website is www.pbeditorialservices.com.